--flat is the cli option, but there's also "flat": true support in package.json. Used at the top level this forces a flat install, but used in a dependency it m

--flat is the cli option, but there's also "flat": true support in package.json. Used at the top level this forces a flat install, but used in a dependency it means that that package requires a flat install and it throws an error if it's not. This means that HTML imports and ES6 modules can force flat installs and start moving the front-end package ecosystem in that direction.